Automatic camera shutter mechanism



AUTOMATIC CAMERA SHUTTER MECHANISM 2 Sheets-Sheet 1 Filed Jan. 28, 1959 INVENTORS a! I I ATTO EYS Aug. 8, 1961 J. w. LOTHROP ETAL 2,995,073

AUTOMATIC CAMERA SHUTTER MECHANISM 2 Sheets-Sheet 2 Filed. Jan. 28, 1959 FIG. 6

mmvrozes A ORNEYS United States Patent AUTGMATIC CAMERA SHUTTER MECHANISM John W. Lothrop, Westwood, Edward M. Purcell, Cambridge, and Sidney B. Whittier, Concord, Mass., assignors to Polaroid Corporation, Cambridge, Mass., a

corporation of Delaware Filed Jan. 28, 1959, Ser. No. 789,681 6 Claims. (Cl. 95-10) This invention relates to photography and particularly to a novel photographic shutter having an automatic photoelectric control of shutter speed.

The present application is a continuation-in-part of copending application Serial No. 711,331, filed January 27, 1958.

Since the development of the photocell, particularly of the type known as the photovoltaic cell, many efforts have been made to utilize the electrical output of a photocell as a parameter for exposure control of photoelectric apparatus. Because until recently the power output of such cells has been considered too minute to provide the force necessary to move shutter elements, efforts had been directed primarily toward coupling photocell output to diaphragm aperture control or, where shutter speed control was desired, various schemes for amplifying the power output to operate shutter speed control means had been developed. However, the devices employing a mechanical method for such amplification have had serious difficulties due to the effect of mechanical friction upon their operation.

This invention, therefore, comprehends a photographic shutter means which includes a photosensitively controlled, pneumatic, variable shutter time delay means having a minimum of frictional elements.

A further object of this invention is to provide an automatic shutter having delay means for controlling the speed of said shutter in accordance with electrical signals from a photosensitive means, said delay means comprising an elastic enclosure having an aperture therein, and means controlling fluid flow through said aperture responsive to electrical signals. a

A further object of this invention is to provide in such a shutter, means for setting said delay means and being operable in a predetermined time sequence prior to actuation of said shutter.

Another object of this invention is to provide a shutter automatically responsive to intensities of light intended to be transmitted therethrough and comprising, in combination, a photosensitive means for producing electrical signals in accordance with said light intensities, an ex posure aperture, -a shutter element for covering and uncovering said exposure aperture, pneumatic means attached to said shutter element for moving said shutter element to cover and uncover said exposure aperture, said pneumatic means comprising an elastic collapsible and expansible enclosure having an opening therein, movable valve means for controlling movement of fluid through said opening in accordance with said electrical signals, the time rate of expansion of said enclosure being a function of the rate of fluid flow through said opening, and means for presetting said valve means at a position of control determined by said signals before actuation of said shutter element for uncovering said exposure aperture.

Another object of this invention is to provide a method of operation of a photoresponsive shutter mechanism including the steps of presetting the exposure time interval of said mechanism while in close proximity to a photographic subject and effecting exposure by said mechanism when removed to a position further from said subject.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

Patented Aug. 8, 1961 The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts, and the method involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic plan view, partly in fragmentary section, showing the associated elements of the invention;

FIG. 2 is a plan view of some of the elements of FIGURE 1 in a set position;

FIG. 3 is a cross section taken substantially along the line 33 of FIGURE 1;

FIG. 4 is an enlarged schematic plan view of the valve orifice shown in FIGURE 1;

FIG. 5 is a plan view of the mechanism of FIG. 2 showing a presetting clamp mechanism in operational relation to the other parts thereof; and

IG. 6 is a cross-sectional view of FIG. 5 taken along the line 66.

There is shown in the drawings one form of the invention comprising means for defining an exposure aperture, movable shutter means for covering and uncovering said aperture, means for actuating the shutter means, and means for controlling the speed of movement of the shutter means in accordance with light intensities. These various means, which preferably may be hermetically sealed, cooperate in a novel manner with one another to establish an exposure, the exposure being understood to mean the total amount of light which this cooperation allows to pass through the aperture in terms of time, light intensity and effective aperture area.

In the preferred form of the invention the entire mechanism may be hermetically sealed to minimize injurious effects of moisture and dust from the ambient atmosphere upon the operation of the components. This may be accomplished by sealing any junctures of housing portions, providing optical apertures with optically transparent airseals and providing seals for all electrical and mechanical extensions which may be necessarily made through the housing means. If the invention is to be used under circumstances where air-tightness might be undesirable because of difficulties created by differences in barometric pressure between the interior and exterior of the housing means, it is preferred that the housing remain sealed with, however, a vent provided leading into said interior with a filter inserted into the vent to exclude dust and other foreign matter.

Direction of rotation and position of the elements of the mechanism as hereinafter described are those which would be observed viewing the mechanism as in FIGURE 1, wherein is shown a housing means designated general ly at 20, which housing means includes rear portion 22 and front portion 24 (only a fragment of the latter being shown). These portions provide means for defining an exposure aperture, for instance, rear portion 22 is shown as provided with aperture 26, front portion 24 having a similar aperture (not shown) disposed therein and being coaxial with aperture 26. A photosensitive means for generating electrical signals in accordance with light incident thereon, such as a photovoltaic cell shown at 28, which may be of any of the type well known in the art, is preferably mounted on the exterior of front housing portion 24 adjacent the aperture in said front housing portion, with the photosensitive surface of said cell being disposed approximately normal to the optical axis of aperture 26. As a means for temperature-compensating the electrical output of said cell and matching the linearity of cell output with a galvanometer response, there is provided a thermal resistance element such as is shown generally at 29. Cell 28 may be removable for mounting elsewhere and additionally may be provided with means for controlling the light incident upon said photosensitive surface, as for instance, a light-transmitting, lenticular surface cover as shown at 30, honey-comb baffles, louvres or the like. Means such as leads 32 are provided for electrically coupling said cell to components of the inven tion contained within said housing, said leads being preferably introduced into the interior of said housing through means for sealing said housing to exclude contaminants.

In the preferred embodiment of the invention as shown in the drawings, there is provided a means for covering and uncovering aperture 26, said means comprising a single-bladed element, which in the preferred form includes an opening therein. Mounted in the housing, for example, on rear portion 22 is such a means, as for example, planar shutter blade 34, said shutter blade being movably mounted, for example, for pivotal movement about pivot 36 between a rest position and a set position. Blade 34 includes an opening 33 therein, which opening passes over aperture 26 during exposure movement of said blade, i.e., a portion of the pivotal movement of blade 34 from the set position wherein said opening lies to one side of aperture 26 to the rest position, wherein said opening lies to an opposite side of said aperture, thereby offering no obstruction to light passing through the aperture in the front housing portion to and through the exposure aperture 26. Blade 34 is shaped to completely occlude aperture 26 whenever blade opening 38 or any portion thereof does not overlie aperture 26. Blade 34 is provided with an arm portion 40 disposed on the opposite side of the pivotal axis of blade 34 from opening 38. Blade 34 also includes, adjacent the pivotal axis thereof, means such as finger 42 for coupling blade 34 with an actuating means for rotating said blade from rest position to set position. For simplicity and ease in manufacturing, blade 34, as recited, may be manufactured for instance, by stamping as a unit from a fiat sheet of metal.

The actuating means, in engagement with and for rotating blade 34, is preferably of the self-cocking type wherein a single movement of said actuating means both cocks, i.e., moves the blade to the set position, and disengages the blade at set position to allow the blade to return to its normal or rest position, the actuating means reengaging the blade after the blade has so returned. In the preferred embodiment, the actuating means for rotating blade 34 comprises lever 50 pivotally mounted as at 52 to rear housing 22. A portion of lever 50 such as arm 54 may extend through an opening 56 provided in the side of housing to provide means for enabling an operator to rotate lever 50 about pivot 52 in an are defined by means, such as marginal portions 58 and 59 of opening 56, for limiting movement of lever 50. Suitable means for sealing opening 56 may be provided, as by an elastic sheet affixed to the periphery of said opening and snugly fitted about arm 54. Alternatively, the actuating means may comprise an arm attached to an axle extending through front housing portion 24 and fixed to blade 34, thereby eliminating opening 56. As a means for biasing lever 50 in a clockwise direction, there is provided a resilient means such as return spring 60 which is attached at one extremity to rear housing portion 22 as at 62, and at the other extremity of spring 60 to an anchoring means such as stud 64 disposed upon lever 50 between pivot 52 and opening 56. Lever 50 is provided with means such as ar-m extension 66 for cooperating with finger 42 and in slidable engagement therewith for rotating shutter blade 34 from rest position to set position, arm extension 66 being disposed opposite arm 54 with respect to the pivotal axis of rotation of lever 50.

As no exposure is intended to be made during move ment of blade 34 from the rest position to the set position, in the preferred form of the invention auxiliary means are provided to cover aperture 26 during that portion of the movement of said blade from rest position to set position during which opening 38 in blade 34 passes over aperture 26. In the preferred embodiment, said auxiliary covering means comprises shutter blind member 7i) which is attached to and so movable with lever 50 that movement of said lever for rotating blade 34 into said set position moves shutter blind member 70 into covering relation to aperture 26 during that portion of said movement when opening 38 overlies aperture 26. Member 70 includes a planar shutter blind portion 72 which is movable across aperture 26 in a plane parallel to and adjacent to the plane of movement of blade 34. As with the shutter blade 34, and in a similar manner, lever 50 and its associated portions including shutter blind member 70, for the sake of simplicity in manufacture, assembly and operation, may be manufactured, for instance, by stamping as a unit from a metal sheet. Extending approximately perpendicularly to the plane of movement of and being attached to lever 50 adjacent pivot 52 is a support means such as pin 74.

A means for controlling the speed of pivotal movement of blade 34 from set positon to rest position and therefore, the exposure period, is provided preferably in the form of an elastic collapsible and expansible pneumatic element such as bellows 80. Said bellows in the form shown has a stationary extremity 82 which is attached to a side of housing 20, and has a movable extremity 84 axially movable to allow expansion and collapse of said bellows. Although movable extremity 84 may be pivotally attached to blade 34, in the form shown, it is connected by direct attachment as at 85, to arm portion 40 of blade 34. The direct connection of the blade to the speed control means confers several advantages to this invention over the prior art. It reduces linkages to a minimum, thereby minimizing the inertia of the system and vitrually eliminating any problem of backlash or creep found in complex mechanical linkages. Further, it reduces frictional effects inherent in a complex linkage system, thereby providing for smoother and more positive operation. Extremity 84 is so disposed in the arcuate path of movement of arm 40 that clockwise rotation of blade 34 collapses bellows 80. After bellows has been collapsed, expansion of said bellows by, for instance, atmospheric pressure, rotates arm portion 40 in a counterclockwise direction. Bellows 80 includes an aperture 86 therein located adjacent stationary extremity 82; otherwise said bellows is preferably pneumatically sealed. Bellows 80 is preferably provided in a cylindrical form having an elastic structural material such as rubber, but is in no sense limited to either this form or material. It should be noted that, as in FIG- URE 1, a resilient means comprising spring 87 may be attached at one extremity to tension-adjusting plate-and bolt assembly 88 which is attached to housing 20, the other extremity of spring 87 being connected to moving end 84 of bellows 80. Hence, the counterclockwise rotation of arm portion 40 may be under the combined bias of spring 87 and expanding bellows 80 or any combination of the two or the bellows alone. It is, however, preferable that the resiliency of spring 87 be substantially in excess of that of bellows 80 to provide for more accurate control of the movement of blade 34.

The expansible and collapsible pneumatic member of this invention, in the preferred embodiment, comprises elastic bellows 80 which exhibits several distinct advantages over other mechanical amplifying means for retarding shutter blade speeds. It is simple in construction, easy to operate and has a comparatively long, trouble-free operating life. In the use of such bellows, frictional factors are minimized, there being no piston to cylinder wall contact, for instance. A bellows is more easily sealed to exclude dirt and other contaminants; no lubricants are necessary as might well be required as with a piston and cylinder arrangement; a superior internal air-seal is easily obtained, there being no pistonskirt to cylinder-wall by pass tolerances to consider; there being a minimum of moving parts, manufacturing problems are consequently simplified; the inertia and friction between moving parts may be kept to a minimum so that response and sensitivity are optimal, there being no need of linkages such as piston to piston rod; and the bellows may be, as shown, directly attached to a shutter blade, any distortion of the bellows, due to lack of a pivotal connection, having no serious effect on the operation of the mechanism. Furthermore, the bellows itself may provide the only means necessary, through its inherent resiliency, for moving the shutter blade from said set position to said rest position.

Means for controlling the rate of expansion or collapse of the pneumatic member comprises means for transmitting a fluid from and to said member, and means for controlling fluid flow through the last-named means and being coupled with and responsive to electrical signals from the photosensitive means. As a means for transmitting a fluid, pipe 90 is attached at one extremity thereof to aperture 86 in bellows 80, the juncture of said pipe and said bellows being pneumatically sealed. To provide for desirable fluid flow characteristics, pipe 90 preferably comprises a member having no interior surface discontinuities such as angled bends. Attached to the other extremity of pipe 90 is a means for controlling the fluid flow through said pipe comprising an element such as block 92 (shown in FIG. 3) having a passageway 94 therein. Pipe 90 is attached and sealed to one end of passageway 94, the other end of said passageway being shaped to present a fluid aperture 96 at a surface of block 92. Aperture 96 preferably has a bowtie cross section configuration as shown in FIG. 4, the total area of said cross section being a function of a maximum fluid displacement of the interior of bellows 80. The minimum width of the aperture cross section configuration is preferably in the nature of .010 inch, the maximum width at each end of said cross section being preferably about 0.1 inch. Means for controlling fluid flow through pipe 90 also comprises valve means coupled to cell 28 for cooperating with fluid aperture 96 toproduce an effective fluid orifice which is variable in area responsively to electrical signals from said cell. Said valve means may comprise, for instance, a fluid obstructing member displaceable by means such as galvanometer element, a solenoid, or such other well known electrical apparatus as may translate electrical signals from cell 28 into mechanical displacements for varying fluid flow through aperture 96.

In FIG. 3, the valve means is shown as galvanometer element 100 which comprises the usual field magnet 102, rotatable field coil 104, spring 106, and a vane 108 so attached and rotatable with field coil 104 that the plane of movement of vane 108 is adjacent to and parallel with that portion of the surface of block 92 in which aperture 96 is formed, the clearance provided between block 92 and vane 108 being only sufficient to allow free rotation of said vane without binding. Vane 108 is shaped to provide an opening therein such as an arcuate slit 110, which varies continuously, for instance, from a maximum width of .2 inch to a minimum width of .010 inch, and having an arcuate length of approximately the rotational displacement of coil 104 for a predetermined range of light intensities. Vane 108 preferably comprises a thin resilient sheet material such as aluminum, berylliumcopper alloy or steel. As shown in FIG. 4, slit 110 and aperture 96 are so disposed relative to one another that an arcuate axis A-A lying midway between the sides of slit 110 intersects BB of aperture 96 at the most constricted area of aperture 96 regardless of the rotational positon of coil 104. As the most satisfactory fluid flow characteristics may be obtained with an orifice having a circular cross section, this dispositon of slit 110 and aperture 96 provides a variable orifice which preferably approximates the optimal cross section configuration over a range of size variations. It should be noted that, in the disposition described, the orifice thus provided is defined on two sides by the configuration of aperture 96 and on two other sides by the configuration of slit 110. Coil 104 is mounted inside magnet 102 for pivotal movement and is provided with resilient means such as spring 106 for biasing said coil in a clockwise direction. At a predetermined minimal light intensity, the bias imposed on coil 104 by spring 106 will urge said coil to a position at which the effective orifice is at a maximum. For other light intensities incident on photosensitive means 28, coil 104 will assume a corresponding position of equilibrium determined by the oppositon of the bias of spring 106 against the magnetic moment imposed by an interaction of the field magnet 102 and coil 104 through which the output of photosensitive means 28 is led. Means for limiting the total excursion of vane 108 is provided as by stop pins 112 and 114, thus providing positions of vane 108 at which the effective orifice has maximal and minimal cross-sectional areas. While the preferred form of this invention includes pipe and block 92, opening 86 in stationary extremity 82 of bellows 80 may be shaped to provide the preferred bowtie aperture configuration, and galvanometer and vane 108 may be mounted then with respect to opening 86 to obtain the desired means for controlling the rate of expansion of bellows 80. J

Inasmuch as vane 108 is easily rotated and it is possible to disturb the position thereof relative to fluid aperture 96 by vibrations or other physical forces, it is desirable in the preferred form of the invention to provide means for holding said vane stationary during exposure movement of blade 34. As shown in FIGURE 1, there is provided such a means which may take the form, for instance, of flat resilient clamping member 120 (shown only in fragment), said member being attached to housing portion 22 and extending therefrom toward vane 108. Member 120 is biased by its own resiliency for fnactional engagement with vane 108 to clamp said vane between extremity 122 of member 120 and block 92. As shown, however, member 120 is so slidably and releasably supported by pin 74 that extremity 122 is suspended for a distance above vane 108 just sufliciently to allow said vane to rotate freely thereunder. Extremity 122 preferably includes an opening 124 therein, said opening being so disposed as to overlie fluid aperture 96 and being so dimensioned as to have a minimal crosssectional area in excess of the area of the maximum orifice presented by the combination of vane slit and fluid aperture 96.

The shutter mechanism herein disclosed may be used in combination with any of the conventional diaphragms well known in the art, either the manually adjustable variety or the photoresponsive type. It is, however, preferable to use a diaphragm having a fixed aperture in order to dispense with exposure control adjustment functions by an operator.

In operation, from a rest position of lever arm 50 wherein said lever arm is positioned adjacent marginal portion 59 of opening 56 in housing 20, force applied by an operator rotates arm 50 in a counterclockwise direction against the bias of return spring 60. The rotary movement of arm 50 about pivot 52 is slidably transmitted to finger 42 by arm extension 66 to rotate shutter blade 34 in a clockwise direcion about pivot 36 from a position of rest to a set position. As arm 50 is thus rotated counterclockwise and blade 34 rotates accordingly clockwise, opening 38 in blade 34 is brought into an uncovering position wherein said opening overlies and exposes aperture 26. The rotation ofarm 50 is accompanied by an equal rotation of attached shutter blind 70 which is so disposed angularly relative to shutter blade 34 that when the opening in said blade reaches said uncovering position, shutter blind 70 has been moved into a covering relation to exposure aperture 26 excluding light therefrom. As the force rotating arm 50 counterclockwise continues, blade 34- arrives at a set position at which the arcuate path of arm extension 66 no longer intersects the arcuate path of finger 42, and arm extension 66 disen ages from said finger allowing said finger and blade 34 to rotate freely counterclockwise under the bias of bellows 80 and spring 87. It should be noted that under certain circumstances it would be desirable to prevent premature re-engagement of finger 42 and arm extension 66. Suitable latch means for temporarily restraining arm extension 66 in a disengaged position may then be provided.

It should be noted that, in the form shown, both arm extension 66 and finger 42 are preferably so dimensioned that they are disengageable from one another after a countereclockwise rotation of arm 50 from rest position through a predetermined actuating angle, for example, of 20 degrees. Pin 74 is normally located on arm 50 in slidable support of member 120 when arm 50 is in rest position. Pin 74; is preferably so located on arm 50 relative to member 120 that upon counterclockwise rotation of arm 56 from rest position through a predetermined clamping angle, for instance '10 degrees, pin 74 is slidably moved to a position at which member 120 is no longer slidably supported on pin 74, and member 120 is free to so move under its own resiliency into engagement with vane 108 that the vane is releasably retained in a fixed position at least during movement of shutter blade 34 from its set to rest position. The retention of the vane thus sets the shutter speed according to the equilibrium position which vane 108 has assumed responsively to signals from the photocell. By thus cating pin 74 so that the clamping angle is substantially less than the actuating angle and said clamping angle is traversed during the first part of movement of arm 50 from rest position, it will be seen that rotation of arm 56 to an intermediate position, determined by the clamping angle, releases member 12% for clamping vane 108 while yet maintaining engagement with the shutter blade. Arm 50 must then be rotated through an additional angle to complete rotation through the predetermined actuating angle in order to release the shutter blade to eifect exposure.

This arrangement, which allows the vane to be clamped prior to exposure movement of the shutter blade, permits advantageous delay in a method of use of the invention for photographic purposes. As hereinbefore stated, a photosensitive means such as cell 23 is preferably mounted on the exterior of front housing portion 2 with the photosensitive surface of cell 28 being disposed approximately normal to the optic axis of aperture 26. When the shutter mechanism is incorporated in a photo graphic device such as a camera, surface cover 30 across cell 28 preferably limits the angle of light incident upon the photosensitive surface of cell 28 to the field of view of the lens system of the camera. As photocells usually integrate the total brightness of the field of view, it is apparent that there will be a number of suitations wherein the exposure time interval determined by the photocell will be correct for the brightness of the total field of view of the camera, but erroneous with respect to a particular photographic subject which forms a portion of the total field. A typical example would be where it is desired to photograph a person against a background of a brightly sunlit beach. If, for instance, it were desired that the image of the person occupy of the area of the resultant photograph, it is obvious that the exposure would generally be incorrect for obtaining the best picture of the person. To achieve proper exposure under such circumstances, the usual photographic procedure is to measure the light reflected from the person by means such as a photometer placed in such close proximity with the individual that the meter reading indicates light refiected from the person only. Ordinarily, to accomplish this with a shutter mechanism incorporating a photocell would be difficult because, upon removal of the camera to the proper distance for the desired photograph, the total scene brightness seen by the photocell would again change the exposure time interval setting to an incorrect value. However, the operator of a camera which includes the invention may bring the camera into close proximity to a photographic subject whereby the subject subtends the greater portion of the field of view of the camera. By then rotating arm 50 through the clamping angle the operator may effectively clamp vane 168 in a position determined in accordance with the light incident on cell 23 while cell 28 is in such close proximity. After the vane is thus clamped, the operator may then at his convenience take up another position further re moved from the subject wherein the photographic subject subtends a substantially smaller and desired portion of the field of view of the camera. By then completing the rotation of arm 50 through the entire actuating angle, the operator may effect an exposure, the time interval of which has thus been preset by the prior clamping of the vane. Alternatively, as a means for clamping vane 108 during exposure movement of blade 34, member 120 may be so disposed relative to said vane as to provide adequate clearance for movement of said vane when member 120 is in an unsupported position. Pin 74 may then be disposed to provide means for forcing member 120 against vane 108 when finger 4-2 and arm extension 66 disengage. The latter embodiment would have the advantage of providing a clamping mechanism which need be only resilient enough to return to a rest position.

Photovoltaic cell 28 translates light incident thereon into electrical signals proportioned to light intensities and said signals are introduced into field coil of element 106 causing coil 104 to rotate about its pivotal axis to an equilibrium position to determine the effective orifice provided by the combination of slit 110 and fluid aperture 96. As the rate of fluid flow through said orifice determines the speed of movement of blade 34, the light incident on cell 28 establishes blade speeds.

It is preferable to employ the rate of expansion of bellows 80, as the independent variable for controlling shutter speed, although the rate of contraction also could be used as the controlling parameter. The expansion of belows causes fluid such as air to be drawn into said bellows through said orifice; the pressure differential caused by the inward movement of air will force vane 108 against block 92, thus creating an air seal and minimizing leakage between said vane and said block Also, inward air fiow through said orifice is less turbulent than an outward flow and hence provides a smoother and more accurate mechanism.

Numerous other modifications of this invention will be apparent to those skilled in the art in view of the teachings herein.

Since certain changes may be made in the above apparatus and method without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electrical signals in accordance with light incident thereon, a movable shutter element mounted on said housing in covering relation to said aperture and for uncovering movement across said aperture, means for moving said element, a pneumatic means having a movable portion thereon connected to a portion of said element for controlling the speed of said uncovering movement, the speed of said uncovering movement being a function of the time rate of movement of said portion of said pneumatic means, movable valve means for controlling the time rate of movement of said portion of said pneumatic means, said valve means being movable to a plurality of equilibrium positions responsively to said electrical signals, and means for releasably retaining said valve means in one of said equilibrium positions prior to uncovering movement of said shutter element.

2. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electrical signals in accordance with light incident thereon, a movable shutter blade mounted on said housing in covering relation to said aperture and for uncovering movement across said aperture, means for moving said blade, an elastic pneumatic means having a movable portion thereof attached to a portion of said blade for controlling the speed of said uncovering movement, the speed of said uncovering movement being a function of the time rate of movement of said portion of said pneumatic means, movable valve means for controlling the time rate of movement of said portion of said pneumatic means, said valve means being movable to a plurality of positions of equilibrium in accordance with said electrical signals, means connected to said means for moving said blade and for releasably retaining said valve means in at least one of said positions of equilibrium before said uncovering movement of said shutter blade is effected.

3. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electrical signals in accordance with light incident thereon, a movable shutter element having an opening therein and being mounted on said housing for movement of said opening across said aperture, actuating means engageable with and for so moving said element that said opening moves across said aperture in a first direction, means cooperating with said actuating means for covering said aperture during movement of said opening in said first direction, means for so moving said element in an opposite direction that said opening moves across said aperture thereby producing an exposure, a pneumatic means attached to a portion of said element for controlling the speed of movement thereof in said opposite direction, the speed of said movement in said opposite direction being a function of the speed of movement of a portion of said pneumatic means, movable valve means for controlling the time rate of movement of said portion of said pneumatic means, said valve means being movable to a position of equilibrium responsively to said electrical signals, and means coupled with said actuating means for releasably retaining said valve means in said position of equilibrium before said element is movable in said opposite direction.

4. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electrical signals in accordance with light incident thereon, a movable shutter element mounted on said housing in covering relation to said aperture, said shutter element having an opening therein, actuating means in slidable and releasable engagement with a portion of said shutter element for moving said shutter element between a first position wherein said opening lies to one side of said aperture to a displaced position wherein said opening lies to an opposite side of said aperture, said actuating means disengaging said portion of said element when said element is in said displaced position, resilient means for moving said element from said displaced position to said first position, a pneumatic means having a movable portion thereof connected to a portion of said shutter element for controlling the speed of said movement from said displaced position to said first position,

the speed of said movement from said displaced position to said first position being a function of the time rate of movement of said portion of said pneumatic means, movable valve means for controlling the time rate of movement of said portion of said pneumatic means, said valve means being movable to a plurality of positions of equilibrium in accordance with said electrical signals, resilient retaining means connected to said actuating means and being movable into engagement with said valve means by a portion of the movement of said actuating means for retaining said valve means in at least one of said positions of equilibrium before said actuating means disengages said portion of said element.

5. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electrical signals in accordance with light incident thereon, a movable shutter element mounted on said housing in covering relation to said aperture and for uncovering movement across said aperture, means for moving said element, a pneumatic bellows attached to a portion of said element for controlling the speed of said uncovering movement, the speed of said uncovering movement being a function of the time rate of expansion of said bellows, movable valve means for controlling the time rate of expansion of said bellows, said valve means being movable responsively to said electrical signals, and means for retaining said valve means in a fixed position of control during said uncovering movement.

6. In a photographic device, a photoresponsive shutter mechanism comprising, in combination, a housing means having an exposure aperture therein, a photosensitive means for producing electricm signals in accordance with light incident thereon, a movable shutter element mounted on said housing in covering relation to said aperture, said shutter element having an opening therein, actuating means in slidable and releasable engagement with a portion of said shutter element for moving said shutter element between a first position wherein said opening lies to one side of said aperture to a displaced position wherein said opening lies to an opposite side of said aperture, said actuating means disengaging said portion of said element when said element is in said second position, means cooperating with said actuating means for covering said aperture during that portion of movement of said element from said first position to said second position during which said opening overlies said aperture, means for moving said element from said second position to said first position whereby an exposure is made, said means for moving said element from said second position to said first position comprising a resilient means, one extremity of said resilient means being attached to one side of said housing, the other extremity of said resilient means being attached to an arm portion of said element, an elastic pneumatic bellows, one extremity of said bellows being attached to said arm portion, the other extremity of said bellows being attached to an opposite side of said housing, said bellows having an aperture therein, a movable valve element, means providing a fluid passageway from said movable valve element to said opening in said bellows, and resilient means for retaining said valve means in a fixed position during movement of said element from said second position to said first position, said valve means being electrically coupled with said photosensitive means and movable responsively to said electrical signals, said resilient means being actuated by said actuating arm when said element is in said second position.

References Cited in the file of this patent UNITED STATES PATENTS 2,187,953 Schmidt Jan. 23, 1940 2,188,820 Riszdorfer Jan. 30, 1940 2,206,626 Blechner July 2, 1940 2,800,844 Durst July 30, 1957 2,885,938 Durst May 12, 1959 

